This invention relates generally to pneumatic impact tools such as rivet guns, and, more particularly, to pneumatic impact tools having means for cushioning the successive recoils of the tool's reciprocating hammer piston.
Pneumatic impact tools of this general kind usually include a barrel and a pistol handle, with a hammer piston reciprocating under the force of pressurized air within a working cylinder in the barrel. Forward movement of the hammer piston is stopped by its impact upon a tool attachment that is useful, for example, in installing a rivet. Rearward movement of the hammer piston, on the other hand, is usually stopped by its impact upon a rigid wall at the barrel's rearward end. The resulting periodic rapid decelerations of the hammer piston produce vibrations that are transmitted directly to the user's hand and arm, causing him considerable discomfort. If the impact tool is used over an extended period, this vibration can even cause physical damage.
Several attempts have been made in the past to cushion the periodic recoil of the hammer piston and thereby reduce its harmful physical effects. Some prior tools have, therefore, included coil springs and/or pneumatic air cushions to stop the hammer piston's rearward movement. Although these prior devices have proven generally effective in reducing the magnitude of tool vibration, they are believed to be unduly complicated and subject to frequent breakdowns.
There is a need for a pneumatic impact tool that reliably provides even greater cushioning of the tool's recoiling hammer piston, so as to reduce tool vibration and improve the user's comfort. The present invention fulfills this need.